1. Field of the Invention
The invention is generally related to the area of optical communications. In particular, the invention is related to optical add/drop devices and the method for making the same.
2. The Background of Related Art
The future communication networks demand ever increasing bandwidths and flexibility to different communication protocols. Fiber optic networks are becoming increasingly popular for data transmission due to their high speed and high capacity capabilities. Wavelength division multiplexing (WDM) is an exemplary technology that puts data from different sources together on an optical fiber with each signal carried at the same time on its own separate light wavelength. Using the WDM system, up to 80 (and theoretically more) separate wavelengths or channels of data can be multiplexed into a light stream transmitted on a single optical fiber. To take the benefits and advantages offered by the WDM system, there require many sophisticated optical network elements.
Optical add/drop devices are those elements often used in optical systems and networks. For example, an exchanging of data signals involves the exchanging of matching wavelengths from two different sources within an optical network. In other words, the multi-channel signal would drop a wavelength while simultaneously adding a channel with a matching wavelength at the same network node.
A commonly used optical add/drop device is what is called a three-port device. As the name suggests, a three-port device has three ports, each for a multi-channel signal, a dropped or added signal or a multi-channel signal without the dropped or added signal. FIG. 1A shows a typical design of a three-port device 100. The device 100 includes a first GRIN lens 102, a multi-layer thin film filter 104 and a second GRIN lens 104. In general, a dual-fiber pigtail is coupled to or positioned towards the first GRIN lens 102, and a single-fiber pigtail is coupled to or positioned towards the second GRIN lens 106. Essentially the two GRIN lenses 102 and 106 accomplish the collimating means for coupling an optical signal with multi channels or wavelengths in and out of a common port (C), a transmission port (T), and a reflection port (R). FIG. 1B shows a pair of GRIN lenses (108 and 110 or 112 and 114) used on one side to facilitate the collimating means. In any case, the three-port device 100 is known to have a very low coupling loss from the C-port to both the R-port and the T-port for use as a demultiplexing device, and vise versa as a multiplexing device.
The GRIN lens has a distinct advantage of having a flat end surface for attaching a thin film filter thereto, which is an essential step for assembling a three-port device. However, it is also known that GRIN lenses are expansive. Alternative lenses, such as conventional C-lenses or ball-lenses are being tried. U.S. Patent Application 2003/10103725 shows a three-port device using C-lenses, whereas a R-channel C-lens, a C-lens spacer, a thin film filter, another C-lens spacer, and a T-channel C-lens are all packaged into a piece of tubing. However, it can be appreciated from the following description of the present invention that the minimal insertion loss per the design of U.S. Patent Application 2003/0103725 could be hardly achieved with the proposed assembly process.
Accordingly, there is a great need for improved optical add/drop devices that are amenable to small footprint, broad operating wavelength range, enhanced impact performance, lower cost, and easier manufacturing process.